A77 Will not Record - UK Vintage Radio Repair and Restoration Discussion Forum

badgregory · 29th Nov 2011, 11:52 am

I have an A77 Revox, 4 track, 3.75 and 7.5 ips machine. It plays back perfectly. However when I put it into record, it starts up and then stops a few times, the light in the tape path goes off and on and then the maching stops altogether. Does anyone have an idea what I can do to fix it? All help gratefully received. I have not used the machine for the about five years, and it has been languishing in the loft.

Michael Maurice · 29th Nov 2011, 12:18 pm

Gregory.

The only difference between play and record is that the bias oscillator and record amplifiers are switched on, the mechanics are the same. However it will use more power and that leads me to suspect that the fault lies in the stabilised 21V supply.

If you know what you are doing, measure the 21V both in play and in record, if you find that it drops in record then the power supply isat fault.

There is a preset on the power board P106 which is a 2.5K (nearest is 2.2K) which can cause this.

I'm in Wembley, If you need help send me a PM.

badgregory · 29th Nov 2011, 6:26 pm

I fear that is way past my capabilities. I hoped it would be more simple. I'll PM you. Yours Gregory

badgregory · 29th Nov 2011, 6:31 pm

I can't PM you, according to the system you have no space in your inbox.

Michael Maurice · 1st Dec 2011, 4:07 pm

Gregory brought this machine to me.

I found that C712 in the record Oscillator had gone short circuit.

This decouples the 20V supply. The reason it didn't blow any fuses is because the 20V rail is derived from the 21V supply on the record relay board, via transistor Q601.

29th Nov 2011, 11:52 am	#1
badgregory Retired Dormant Member Join Date: Nov 2011 Location: Ealing. Posts: 3	A77 Will not Record I have an A77 Revox, 4 track, 3.75 and 7.5 ips machine. It plays back perfectly. However when I put it into record, it starts up and then stops a few times, the light in the tape path goes off and on and then the maching stops altogether. Does anyone have an idea what I can do to fix it? All help gratefully received. I have not used the machine for the about five years, and it has been languishing in the loft.

29th Nov 2011, 12:18 pm	#2
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: A77 Will not Record Gregory. The only difference between play and record is that the bias oscillator and record amplifiers are switched on, the mechanics are the same. However it will use more power and that leads me to suspect that the fault lies in the stabilised 21V supply. If you know what you are doing, measure the 21V both in play and in record, if you find that it drops in record then the power supply isat fault. There is a preset on the power board P106 which is a 2.5K (nearest is 2.2K) which can cause this. I'm in Wembley, If you need help send me a PM.

29th Nov 2011, 6:26 pm	#3
badgregory Retired Dormant Member Join Date: Nov 2011 Location: Ealing. Posts: 3	Re: A77 Will not Record I fear that is way past my capabilities. I hoped it would be more simple. I'll PM you. Yours Gregory

29th Nov 2011, 6:31 pm	#4
badgregory Retired Dormant Member Join Date: Nov 2011 Location: Ealing. Posts: 3	Re: A77 Will not Record I can't PM you, according to the system you have no space in your inbox.

1st Dec 2011, 4:07 pm	#5
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: A77 Will not Record Gregory brought this machine to me. I found that C712 in the record Oscillator had gone short circuit. This decouples the 20V supply. The reason it didn't blow any fuses is because the 20V rail is derived from the 21V supply on the record relay board, via transistor Q601.